Using manual flash units on 35mm film compact cameras with Flashmatic
While automatic exposure control is common on newer flash units, many older models work manually. You set the shutter speed and aperture on the camera, working out the latter from the guide number and distance using a dial, scale or table on the flash, or by manual calculation. For example, using a flash unit with a guide number of 24m at a distance of 3m, you'd set the aperture to f/8.

However, some older 35mm film compact and rangefinder cameras with flashmatic control (or SLR cameras with GN lenses) can provide automatic exposure – you set the guide number, and the aperture is coupled to the focusing system and adjusts automatically for different distances.

Guide Number lenses were made by Nikon (45mm f/2.8 GN-Nikkor), Sigma (35mm f/2.8 Flash Auto), Topcon (several 50mm GN-Topcors) and Zeiss (35mm f/2 and 50mm f/2 Blitz Planar for Contarex), which can be used on various SLR cameras.

The flashmatic system can of course be used with any flash that has a manual mode, not just non-automatic ones. There are advantages to this approach compared to the more common automatic systems, as flashmatic isn't affected by light/dark clothing, skin tones or backgrounds, and off-centre subjects. Drawbacks include an often limited range of available guide numbers on the camera, with increased battery consumption and recycling times compared to thyristor auto flash units. The quoted guide numbers on many flash units are slightly "optimistic" by modern standards, so some experimentation may be required to arrive at a more realistic value.

Check below for manual flash units, ideal for use with these flashmatic cameras.